Magnetic tunnel junction structures and methods of manufacture thereof

ABSTRACT

Embodiments of magnetic tunnel junction (MTJ) structures discussed herein employ seed layers of one or more layer of chromium (Cr), NiCr, NiFeCr, RuCr, IrCr, or CoCr, or combinations thereof. These seed layers are used in combination with one or more pinning layers, a first pinning layer in contact with the seed layer can contain a single layer of cobalt, or can contain cobalt in combination with bilayers of cobalt and platinum (Pt), iridium (Ir), nickel (Ni), or palladium (Pd), The second pinning layer can be the same composition and configuration as the first, or can be of a different composition or configuration. The MTJ stacks discussed herein maintain desirable magnetic properties subsequent to high temperature annealing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/351,850 filed Mar. 13, 2019, which will issue as U.S. Pat. No.10,944,050 on Mar. 9, 2021, which claims benefit of U.S. ProvisionalPatent Application No. 62/668,559, filed May 8, 2018, each of which isherein incorporated by reference in its entirety.

BACKGROUND Field

Embodiments of the present disclosure generally relate to fabricatingmagnetic tunnel junction structures for magnetic random access memory(MRAM) applications.

Description of the Related Art

Spin transfer torque magnetic random access memories, or STT-MRAMs,employ magnetic tunnel junction structures in the memory cells thereof,wherein two ferro-magnetic layers are spaced from one another by a thininsulating or “dielectric” layer. One of the magnetic layers has a fixedmagnetic polarity, the other has a magnetic polarity which isselectively changeable between two states. Where the magnetic layershave perpendicular magnetic anisotropy, the polarity of the changeablepolarity layer can be switched between having the same polarity as thefixed polarity layer, or the opposite polarity to that of the fixedpolarity layer, in the depth direction of a stack of film layerscomprising the magnetic tunnel junction or “MTJ” structure. The electricresistance across the MTJ is a function of the polarity of thechangeable polarity layer with respect to the fixed polarity layer.Where the polarities of the two layers are the same in the depthdirection of the MTJ, the electric resistance across the MTJ is low, andwhen they are opposite to one another in the depth direction of the MTJ,the electric resistance across the MTJ is high. Thus, the electricalresistance across the memory cell can be used to indicate a value of 1or 0, and thus store a data value, for example by using the lowresistance state as having the data value of 1, and the high resistancestate as the data value of 0.

Where MTJs are synthetic anti-ferromagnets (SAF) that comprise two ormore ferromagnetic layers separated by a nonmagnetic layer, SAF couplingcan be lost after high temperature processing thereof, for exampleprocessing at temperatures at or above about 400° C.

To form an MTJ stack, a film layer stack including a seed layercomprising platinum (Pt) or ruthenium (Ru) is used to ensure the propercrystalline orientation, here a face cubic centered <111> orientation,in the overlying pinning layers to establish therein perpendicularmagnetic isotropy or PMA. To properly form the MRAM cell, the film stackis annealed at around 400° C. for about 0.5 to 3 hours. However, duringthis annealing, the crystal lattice and resulting crystal and magneticpole orientation in the pinning layers is lost, or at least partiallylost, resulting in a loss of the desired (SAF) coupling.

Thus, there remains a need for an improved MTJ stack.

SUMMARY

The present disclosure generally relates to the design and fabricationof magnetic tunnel junction (MTJ) stacks used for memory cells. In oneexample, a device includes a magnetic tunnel junction stack. Themagnetic tunnel junction stack includes a seed layer in contact with abuffer layer, wherein the seed layer comprises chromium (Cr) and a firstpinning layer in contact with the seed layer. The first pinning layer isformed from a plurality of bilayers, wherein each bilayer of theplurality of bilayers comprises a first interlayer formed from cobalt(Co) and a second interlayer formed from platinum (Pt), iridium (Ir),nickel (Ni), or palladium (Pd). The MTJ stack further includes acoupling layer in contact with the first pinning layer; and a secondpinning layer in contact with the coupling layer.

In another example, a magnetic tunnel junction stack includes: a seedlayer formed on a buffer layer, wherein the seed layer compriseschromium (Cr) and a first pinning layer formed on the seed layer,wherein the first pinning layer comprises a first plurality of bilayers.Each bilayer of the first plurality of bilayers comprises a firstinterlayer formed from cobalt (Co) and a second interlayer formed fromat least one of platinum (Pt), iridium (Ir), nickel (Ni), or palladium(Pd). The MTJ stack can further include a coupling layer formed on thefirst pinning layer; and a second pinning layer formed on the couplinglayer, wherein the second pinning layer comprises cobalt (Co).

In another example, a magnetic tunnel junction stack includes a seedlayer formed on a buffer layer, wherein the seed layer compriseschromium (Cr), and is from 1 Å to 100 Å thick and a first pinning layerformed on the seed layer, the first pinning layer having a thicknessfrom 1 Å to 100 Å, wherein the first pinning layer comprises a firstplurality of bilayers and a first cobalt overlayer formed over the firstplurality of bilayers. The MTJ stack further includes a coupling layerformed between the first pinning layer and the first cobalt overlayer; asecond pinning layer formed on the coupling layer, the second pinninglayer having a thickness from 1 Å to 100 Å thick, wherein the secondpinning layer comprises a second plurality of bilayers; a structureblocking layer formed on the second pinning layer. The structureblocking layer includes at least one of tantalum (Ta), molybdenum (Mo),or tungsten (W). and is from 1 Å to 8 Å thick. The MTJ stack furtherincludes a magnetic reference layer formed on the structure blockinglayer; a tunnel barrier layer formed on the magnetic reference layer;and a magnetic storage layer formed on the tunnel barrier layer.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlyexemplary embodiments and are therefore not to be considered limiting ofits scope, may admit to other equally effective embodiments.

FIG. 1A is a schematic illustration of an example magnetic tunneljunction (MTJ) stack.

FIG. 1B is a flow diagram of a method of fabricating memory devicesincluding magnetic tunnel junction (MTJ) stacks of FIG. 1A and accordingto embodiments of the present disclosure.

FIG. 2A is a schematic illustration of an MTJ stack according toembodiments of the present disclosure.

FIG. 2B is a magnified view of the buffer layer of an MTJ stackaccording to embodiments of the present disclosure.

FIG. 2C is a magnified view of the first pinning layer of an MTJ stackaccording to embodiments of the present disclosure.

FIG. 2D is a magnified view of the second pinning layer of an MTJ stackaccording to embodiments of the present disclosure.

FIG. 2E is a magnified view of an example magnetic storage layer of anMTJ stack according to embodiments of the present disclosure.

FIG. 2F is a magnified view of an example capping layer of an MTJ stackaccording to embodiments of the present disclosure.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

DETAILED DESCRIPTION

Embodiments of the present disclosure relate to magnetic tunnel junction(MTJ) stacks and STT MRAM memory cells and memories. Herein, the MTJstacks are incorporated in a film stack including upper and lowerelectrodes, wherein the MTJ stack is sandwiched therebetween and can beused to form a plurality of memory cells used in magneto-resistiverandom-access memory (MRAM). In each MTJ stack of an MRAM, there are twomagnetic layers, wherein one magnetic layer has a fixed polarity and theother has a polarity that can be switched by imposing a voltage acrossthe layer or applying a current to that magnetic layer. The electricalresistance across the MRAM changes based on the relative polaritybetween the first and second magnetic layers. The first and secondmagnetic layers are referred to herein as a magnetic reference layer anda magnetic storage layer. The memory cells formed from the MTJ stacksoperate when there is a voltage imposed across or a current passedthrough the memory cell. In response to the application of voltage ofsufficient strength, the polarity of the switchable magnetic layer canbe changed. Additionally, the resistivity of the memory cell can bedetermined by measuring the current vs voltage relationship across thememory cell at a relatively low voltage below the threshold required toswitch the magnetic polarity of the magnetic storage layer.

The basic MTJ stack discussed herein is formed using a plurality ofdeposition chambers to deposit thin film layers on a substrate, andultimately pattern and etch those deposited film layers. The depositionchambers used to form the MTJ stack discussed herein includes physicalvapor deposition (PVD) chambers. Here PVD chambers are used to form theplurality of thin film layers of the MTJ stack. The MTJ stack thusincludes a buffer layer, a seed layer on the buffer layer, a firstpinning layer on the seed layer, a synthetic antiferromagnetic (SAF)coupling layer on the first pinning layer, a second pinning layer on theSAF layer, and a blocking layer on the second pinning layer. In the PVDoperations described hereof, an inert or noble gas such as argon (Ar),helium, (He), krypton (Kr), and/or xenon (Xe), is ionized as a plasma inthe sputtering chamber while the chamber is maintained in a vacuumstate. The PVD process chamber further contains at least one sputteringtarget and a substrate disposed facing a generally flat surface of thesputtering target. The sputtering target is coupled to a power supplysuch that it is electrically driven, or self establishes, a cathodicstate in a circuit of the power supply, through the plasma, to ground,for example a grounded portion of the sputtering chamber. The substrateis disposed on a pedestal or other structure in the sputtering chamber,which may be at a floating potential, connected to ground, or may bebiased to form an anode in the cathodic target to generate plasma toanode or ground circuit. The positively ionized portion of the inert gasatoms in the sputtering chamber are electrically attracted to thenegatively biased target, and thus ions of the plasma bombard thetarget, which causes atoms of the target material to be ejected anddeposit on the substrate to a form a thin film composed of the targetmaterial(s) on the substrate.

In order to form a thin film of a compound, a sputtering targetincluding that compound can be used along with an Ar plasma in a PVDchamber. In another example, a plurality of sputtering targets, eachincluding one or more elements of the compound to be formed as a film onthe substrate, are present in the PVD chamber and used with an Ar plasmato form a desired compound. Further in the PVD operations used herein toform layers of the MTJ stack, metal-oxides and metal-nitrides are formedusing either a metal-oxide or a metal-nitride sputtering target. Inalternate embodiments, the metal-oxide or metal-nitride layers areformed in a PVD chamber by sputtering one or more metal sputteringtargets composed of the metal of the metal oxide or nitride while Arplasma and either oxygen (O₂) or nitrogen (N₂) are present in the PVDchamber. In one example, a PVD chamber has a plurality of sputteringtargets disposed therein, each sputtering target in the PVD chamber isbiased by a power supply to establish a negative bias thereon, either bydirect application of a negative DC bias thereto, or by using a waveformto electrically drive or self-establish a cathodic state on the target,or combinations thereof. In this example, a shield inside the PVDchamber is configured to block one or more of the plurality of targetswhile allowing ions of the plasma formed in the PVD chamber to bombardat least one of the targets to eject or sputter target material atomstherefrom to form a thin film on the substrate while protecting othersputtering targets in the chamber from the plasma. In this example, oneor targets are exposed to the Ar plasma, and the sputtering thereof inseries or simultaneously forms the desired film composition on thesubstrate, and a separate PVD chamber is used to form metal-oxide andmetal-nitride layers when O₂ or N₂, respectively, are used in additionto Ar plasma for film layer formation on the substrate.

A PVD system can include one or more PVD sputtering chambers coupled toa central robotic substrate transfer chamber. The central roboticsubstrate transfer chamber is configured to move substrates betweenloading stations coupled thereto and the sputtering chambers connectedthereto. The PVD system is kept at a base vacuum pressure of, forexample, 10 E⁻⁹ Torr, so that the substrate on which the MTJ stack isbeing formed is not exposed to an external atmosphere when the substrateon which the MTJ stack is being formed is moved among and between PVDchambers during fabrication of the MTJ film layer stack thereon. Priorto forming the initial film layer of the MTJ film layer stack on asubstrate, the substrate is degassed in a vacuum chamber and pre-cleanedusing an Ar gas plasma or in an He/H gas plasma in a dedicatedprecleaning chamber connected to the central robotic transfer chamber.During fabrication of the MTJ stack using the one or more PVD chambers,one or more noble or inert sputtering gases such as Ar, Kr, He, or Xecan be disposed in each of the PVD chambers. The gases are ionized toform a plasma in the chamber, and the ions of the plasma bombard thenegatively biased sputtering target(s) to eject surface atoms from thetarget to deposit a thin film of the target material(s) on a substratelocated in the PVD sputtering chamber. In an embodiment, a processingpressure in the one or more PVD chambers can be from about 2 mTorr toabout 3 mTorr. Depending upon the embodiment, the chambers of the PVDplatform are held from −200° C. to 600° C. during fabrication of atleast the seed layer, the first and second pinning layers, the SAF layerand the buffer layer of the MTJ stack.

FIG. 1A is a schematic illustration of a magnetic tunnel junction (MTJ)stack. FIG. 1A shows a conventional MTJ stack 100A that includes asubstrate 102 that has a conductive layer of tungsten (W), tantalumnitride (TaN), titanium nitride (Tin), or other metal layers formedthereof. In some examples, the substrate 102 includes one or moretransistors, bit or source lines, and other memory lines, previouslyfabricated therein or thereon, or other elements to be used in MRAMmemory and previously fabricated or formed thereon. The substrates onwhich the MTJ stacks are formed can have dimensions including a diameterof less than 200 mm, a diameter of 200 mm, a diameter of about 300 mm,about 450 mm, or another diameter, and may have a shape of a circle or arectangular or square panel.

A buffer layer 104 in the conventional MTJ stack 100A is formed on thesubstrate 102 by sputtering one or more targets in a PVD chamber havingthe substrate therein, and here includes one or more layers ofCo_(x)Fe_(y)B_(z), TaN, Ta, or combinations thereof. A seed layer 106formed via sputtering in a PVD chamber over the buffer layer 104. Thebuffer layer 104 is used in the conventional MTJ stack 100A to improveadhesion of the seed layer 106 to the substrate. The seed layer 106 hereincludes platinum (Pt) or ruthenium (Ru) and is formed by sputtering atarget of Pt or Ru, or an alloy thereof, in a PVD chamber having thesubstrate therein. The seed layer 106 can be used to improve adhesionand seeding of subsequently deposited layers in the conventional MTJstack 100A by reducing or eliminating lattice mismatch between thebuffer layer 104 and the seed layer 106.

A first pinning layer 108 is formed on the seed layer 106 by sputtering.The first pinning layer 108 here includes a cobalt (Co) layer, one ormore Co-containing bilayers, or a combination of the cobalt layer andone or more Co-containing bilayers. A synthetic antiferromagnetic (SAF)coupling layer 110 is formed here over the first pinning layer 108 bysputtering. The SAF coupling layer 110 can be formed of ruthenium (Ru),rhodium (Rh), Cr, or iridium (Ir) sputtered from a target thereof. Asecond pinning layer 112 is formed over the SAF coupling layer 110 bysputtering. The second pinning layer 112 is formed here of a singlecobalt (Co) layer, at least one cobalt-platinum bilayer, or acombination of the cobalt layer and the one or more Co-containingbilayers, such as a Co—Pt bilayer, formed by sputtering a targetcomposed of Co, Pt, or Co—Pt, respectively. The SAF coupling layer 110is located between the first pinning layer 108 and the second pinninglayer 112 and causes surface atoms of the first pinning layer 108 andthe second pinning layer 112, when exposed to a magnetic field, to alignwith surface atoms of the SAF coupling layer 110, thereby pinning theorientation of the first pinning layer 108 and the second pinning layer112. The first pinning layer 108 and the second pinning layer 112 eachexhibit similar magnetic moments, and will thus react similarly when anexternal magnetic field is applied to the conventional MTJ stack 100A.The SAF coupling layer 110 maintains an anti-parallel alignment of themagnetic moments of the first pinning layer 108 and second pinning layer112.

A structure blocking layer 114 is formed over the second pinning layer112, and here includes tantalum (Ta), molybdenum (Mo), tungsten (W), orcombinations thereof. The structure blocking layer 114 is employedbecause of its crystalline structure, which differs from the crystallinestructure of the first pinning layer 108 and second pinning layer 112.The structure blocking layer 114 prevents against formation of a shortcircuit between the conventional MTJ stack 100A and metallic contactsthat can be coupled to the conventional MTJ stack 100A to form MRAMmemory cells.

Further in the conventional MTJ stack 100A, a magnetic reference layer116 is formed over the structure blocking layer 114 by sputtering in aPVD chamber. A tunnel barrier layer 118 is formed over the magneticreference layer 116 and a magnetic storage layer 120 is formed over thetunnel barrier layer 118. Each of the tunnel barrier layer 118, themagnetic reference layer 116, and the magnetic storage layer 120 areeach formed by sputtering in one or more PVD chambers in the presence ofan Ar plasma. The magnetic reference layer 116 and the magnetic storagelayer 120 each include a Co_(x)Fe_(y)B_(z) alloy which may vary incomposition. Additionally, the magnetic storage layer 120 can includeone or more layers of Ta, Mo, W, or Hf, or combinations thereof. Thetunnel barrier layer 118 includes an insulating material, and can befabricated from a dielectric material such as MgO. A composition and athickness of the tunnel barrier layer 118 are selected so as to create alarge tunnel magnetoresistance ratio (TMR) in the tunnel barrier layer118 of the conventional MTJ stack 100A. The TMR is a measurement of achange in resistance in the conventional MTJ stack 100A from theanti-parallel state (R_(ap)) to the parallel state (R_(p)) and can beexpressed as a percentage using the formula ((R_(ap)−R_(p))/R_(p)). Whena bias is applied to the conventional MTJ stack 100A, the tunnel barrierlayer 118 is traversed by spin-polarized electrons, this transmission ofelectrons through the tunnel barrier layer 118 results in electricalconduction between the magnetic reference layer 116 and the magneticstorage layer 120.

A capping layer 122 is formed, sputtering in a PVD chamber, on themagnetic storage layer 120 and here includes a plurality of interlayers.The plurality of interlayers of the capping layer 122 includes a firstcapping interlayer 122A fabricated from a dielectric material such asMgO. A second capping interlayer 122B including a metallic material suchas Ru, Ir, Ta, or combinations thereof, is formed over the first cappinginterlayer 122A. The first capping interlayer 122A acts as an etch stoplayer for hard mask etching and protects the MTJ stack 100A fromcorrosion. The second capping interlayer 122B is configured toelectrically communicate with transistors or contacts when theconventional MTJ stack 100A is later patterned, as shown in FIG. 1B anddiscussed below. A hardmask layer 124 is formed in a PVD chamber bysputtering, and is formed over the second capping interlayer 122B toprotect the conventional MTJ stack 100A and can be patterned duringsubsequent operations.

FIG. 1B is a flow diagram of a method 100B of fabricating memory devicesthat include an MTJ stack 100A and the MTJ stacks fabricated accordingto embodiments of the present disclosure and shown in FIGS. 2A-2F. Themethod 100B is executed in part a plurality of PVD chambers of a PVDsystem that are configured to deposit thin film layers by sputtering.The substrate 102 can be moved among and between sputtering chambers viathe central robotic transfer chamber of the PVD system to form variousthin film layers, including those in FIG. 1A and those shown anddiscussed below that are fabricated according to embodiments of thepresent disclosure. In another example, as discussed above, a pluralityof sputtering targets are disposed in a PVD chamber and a shield insidethe PVD chamber is configured to selectively protect the plurality ofsputtering targets from plasma exposure or expose a target thereto. Theshield is rotated at different operations of the method 100B to exposetwo or more targets, in series or simultaneously, to the plasma in thePVD chamber.

The layers of FIG. 1A are thus referenced herein with respect to themethod 100B. The operations of the method 100B are performed using oneor more gases including argon (Ar), helium (He), krypton (Kr), xenon(Xe), oxygen (O₂), or nitrogen (N₂) in the PVD chamber or chambers. Theprocessing pressure in the PVD chambers during the method 1006 can befrom about 2 mTorr to about 3 mTorr. Depending upon the embodiment, aPVD chamber can be held from −200° C. to 600° C. during fabrication ofthe pinning and seed layers of the MTJ stack.

The substrate 102 can be moved among and between PVD chambers dependingupon the composition of the sputtering target(s) used for each layer ofthe MTJ stack 100A, or, as discussed herein, a plurality of targets arecoupled to a power supply and a shield is configured to selectivelyprotect some of the targets, such that one or more targets are exposedin series or simultaneously to form the desired film composition, orboth methodologies can be performed. During sputtering in the PVDchamber, the Ar ions of the plasma bombard the one or more exposedsputtering targets, causing surface atoms of the sputtering targets tobe ejected and deposit as a thin film on the substrate. In the method1006, at operation 128A, a substrate such as the substrate 102 in FIG.1A undergoes operations including degassing, and pre-cleaning in an Argas plasma or in an He/H plasma, and is moved between process chambersthrough or via a central robotic substrate transfer chamber. Atoperation 128B, the substrate 102 is transferred from the centralrobotic substrate transfer chamber to a PVD chamber of a plurality ofPVD chambers. Subsequently, at operation 130, the buffer layer 104 isdeposited on the substrate 102 by sputtering in the target of the PVDchamber. A power from 1 kW to 100 kW is applied to the one or more PVDchambers discussed herein to ionize a portion of the Ar and form theplasma used in the operation 130. The ejected surface atoms of thetarget are deposited on the substrate 102 to form the buffer layer 104.During formation of the buffer layer 104 at the operation 130, asputtering target or targets including Co_(x)Fe_(y)B_(z), TaN, and/or Taare used in the PVD chamber along with Ar plasma to form the bufferlayer 104. In an embodiment where the buffer layer 104 is or includesTa, the buffer layer 104 is sputtered in a PVD chamber using a Ta targetand Ar plasma. In an example where the buffer layer 104 is or includesTaN, the operation 130 is performed when nitrogen gas (N₂) is present inthe PVD chamber along with the Ar plasma and a Ta sputtering target toform the TaN buffer layer 104. In another example where the buffer layer104 is or includes TaN, the operation 130 is performed in a PVD chamberusing a TaN sputtering target and Ar plasma to form the TaN buffer layer104. During formation of the buffer layer 104 and subsequent layers, theone or more PVD chambers used are maintained at vacuum pressure.

Subsequently, in operation 132, the seed layer 106 is deposited on thebuffer layer 104 by sputtering a target in a PVD chamber. In anembodiment of operation 132, the seed layer 106 is formed in the samePVD chamber as the PVD chamber used to form the buffer layer 104, usinga different sputtering target than the sputtering target used to formthe buffer layer 104. In an example of the method 100B according toembodiments of the present disclosure, the seed layer 206 shown in FIG.2A below can be fabricated at operation 132 in a PVD chamber using Arplasma and one or more sputtering targets. FIG. 2A shows a coordinatesystem having an x-axis 226 that is perpendicular to a y-axis 228. Thethicknesses discussed herein can be measured in the direction of they-axis 228. In one example of the formation of the seed layer 206, thesputtering targets in the PVD chamber used to form the seed layer arecomposed of Cr, or a combination of Cr and one or more of Ni, Fe, Ru,Ir, Co. In another example, the sputtering target(s) used in the PVDchamber at operation 132 are composed of one or more alloy targetsincluding NiCr, NiCrFe, RuCr, IrCr, CoCr, or combinations thereof. Theseed layer 206 can be formed to a thickness of 100 Å or less. In oneexample, the seed layer 206 includes NiCr and is fabricated in the PVDchamber using an NiCr target. In this example, Ar is introduced into thePVD chamber at a flow rate of about 5 sccm-60 sccm, and the flow rate ofAr into the chamber is about 25 sccm in some examples. In anotherexample, the Ar is introduced into the PVD chamber at a flow rate from10 sccm to 40 sccm, and, in some examples, at a flow rate of 25 sccm. Apower of about 50 W-1200 W is applied to the sputtering target at anegative voltage when the Ar is present to form the plasma used forsputtering. In some examples, the power applied to the sputtering targetat a negative voltage is from 100 W to 800 W, and in another example,the power applied to the sputtering target is about 500 W.

The first pinning layer 108 is deposited on the seed layer 106 atoperation 134 by sputtering a target in a PVD chamber. The first pinninglayer 108 is shown as an example in the conventional MTJ stack 100A, andcan be formed at operation 134 in a PVD chamber by sputtering one ormore targets in the presence of Ar plasma. In an example where the firstpinning layer 108 is Co, a Co sputtering target is used in the presenceof Ar plasma in the PVD chamber. In an example where the first pinninglayer 108 includes one or more bilayers of cobalt and another element,the operation 134 uses a Co sputtering target and another sputteringtarget composed of the other element of the bilayer. Depending upon theembodiment, the Co sputtering target and the sputtering target of theother metal can be sputtered in the presence of Ar plasma in the samePVD chamber or each layer of the bilayer can be formed in separate PVDchambers.

In an example according to embodiments of the present disclosure, afirst pinning layer 208 as shown in FIG. 2A and FIG. 2C is formed usinga PVD chamber at operation 134. In this example, the first pinning layer208 is formed in a PVD chamber at operation 134 using xenon (Xe) orargon (Ar) that is introduced the PVD chamber at a flow rate of about 2sccm-40 sccm while a power from 50 W to 10000 W is applied to the targetat a negative voltage to form a plasma. In another example, the Xe or Aris introduce to the PVD chamber at a flow rate from 5 sccm to 20 sccm,and, in some examples, at a flow rate of 10 sccm. In another example,the power applied to the sputtering target is from 100 W to 800 W, and,another example, the power applied to the sputtering target can be 400W. Depending upon a composition of the first pinning layer 208, Xe canbe used in the sputtering operation in the PVD chamber at operation 134since it is a heavier gas than Ar, and thus yields ions with higheratomic weights than the ions formed using Ar or other, lighter, gases,and thus bombards the target with more energy. In one example of thefirst pinning layer 208 in the present disclosure, Xe, Ar or a mixturethereof is introduced into the PVD chamber at a flow rate from about 10sccm and a power of 400 W is applied to the target at a negative voltageto form an Ar or Xe plasma. In one example, the first pinning layer 208is fabricated from cobalt (Co) as a single layer from about 1 Å to about18 Å thick by sputtering a Co target. In another example, the firstpinning layer 208 is fabricated from one or more bilayers of variousmaterials as shown in FIG. 2C. In various embodiments, a bilayer used toform the first pinning layer 208 includes a first interlayer of Co and asecond interlayer of another element. The bilayer of the first pinninglayer 208 can be formed at operation 134 in a PVD chamber which includesa plurality of targets including the Co target and a target formed fromthe other element, or in separate PVD chambers, one PVD chambercontaining a Co target and the other PVD chamber containing a target ofthe other element. In the example where the plurality of targets aredisposed in a single PVD chamber in the presence of an Ar plasma and/orXe plasma, each of the Co target and the target of the other metal canbe selectively exposed using the shield discussed herein to form the Cointerlayer of the bilayer and to form an interlayer of the other elementto form a resultant bilayer. These depositions can be repeated atoperation 134 for a plurality of iterations to form a plurality ofbilayers of the first pinning layer 208. The SAF coupling layer 110 isdeposited on the first pinning layer 108 at operation 136 by sputteringa target of Ru, Cr, Rh, or Ir in the presence of an Ar plasma in a PVDchamber. The second pinning layer 112 is deposited on the SAF couplinglayer in a PVD chamber at operation 138. In one example, the secondpinning layer 112 is formed of Co using a Co target and an Ar plasma inthe PVD chamber. In another example, the second pinning layer 112includes a bilayer, and may or may not include a Co layer formed incontact with the bilayer. In this example, the second pinning layer 112is formed in a PVD chamber using a Co sputtering target and a secondmetal sputtering target, and a shield is adjusted to expose each of theCo and second metal sputtering targets separately, in at least oneiteration, to form one or more bilayers of the second pinning layer 112.In other examples, each layer of the bilayer of the second pinning layer112 can be formed in a different PVD chamber, where one PVD chamberincludes a Co sputtering target and the other PVD chamber includes asputtering target of the second metal.

The SAF coupling layer 110 is deposited on the first pinning layer 108at operation 136 by sputtering a target of Ru, Cr, Rh, or Ir in thepresence of an Ar plasma in a PVD chamber. The second pinning layer 112is deposited on the SAF coupling layer in a PVD chamber at operation138. In one example, the second pinning layer 112 is formed of Co usinga Co target and an Ar plasma in the PVD chamber. In another example, thesecond pinning layer 112 includes a bilayer, and may or may not includea Co layer formed in contact with the bilayer. In this example, thesecond pinning layer 112 is formed in a PVD chamber using a Cosputtering target and a second metal sputtering target, and a shield isadjusted to expose each of the Co and second metal sputtering targetsseparately, in at least one iteration, to form one or more bilayers ofthe second pinning layer 112. In other examples, each layer of thebilayer of the second pinning layer 112 can be formed in a different PVDchamber, where one PVD chamber includes a Co sputtering target and theother PVD chamber includes a sputtering target of the second metal.

In one example of a second pinning layer 212 according to embodiments ofthe present disclosure as shown in FIGS. 2A and 2D, the second pinninglayer 212 is deposited in a PVD chamber at operation 138 using Ar and/orXe gas, depending upon the material being sputtered. In an embodiment ofthe present disclosure, the second pinning layer 212 is fabricated atoperation 138 as a single layer of cobalt (Co) using a Co sputteringtarget in the presence of Ar plasma or a plasma comprised of Ar and Xe.In another example, the second pinning layer 212 includes a bilayer thatincludes a first interlayer formed from Co and a second interlayer ofone or more second metals such as Pt, Ir, Ni, or Pd. In another example,which can be combined with other examples herein, the second pinninglayer 212 can be formed of a single Co layer alone or in combinationwith at least one bilayer of a first interlayer of Co and secondinterlayer of at least one different metal. In this example, the secondpinning layer 212 is formed in a PVD chamber using a Co sputteringtarget and a second metal sputtering target, and a shield is adjusted toexpose each of the Co and second metal sputtering targets separately inat least one iteration to form one or more bilayers of the secondpinning layer 212. Xenon can be used for depositing the second pinninglayer 212 when metals such as Pt are used to form the second pinninglayer 212 since Xe is a heavier gas than Ar and can thus interact withheavier metals including Pt more effectively during sputtering processesin a PVD chamber. In an embodiment where Xe is used, the Xe gas isintroduced into the PVD chamber at a flow rate from about 2 sccm toabout 40 sccm, or from 5 sccm to 20 sccm, and, in some embodiments, theXe gas is introduced into the PVD chamber at a flow rate of about 10sccm. During the formation of the second pinning layer 212, a power from50 W to about 1000 W is applied to the target at a negative voltage toform and maintain the Ar and/or Xe plasma. In some examples, a powerfrom 100 W to 600 W is applied to the target at a negative voltage toform and maintain the Ar and/or Xe plasma, and, in some embodiments apower of about 200 W is used.

The structure blocking layer 114 is formed at operation 140 in a PVDchamber that comprises sputtering targets including Ta, Mo, and/or W,depending upon an intended composition of the structure blocking layer114. When two or more sputtering targets of Ta, Mo, and W are used, eachtarget may be used in a separate PVD chamber, or the two or moresputtering targets can be sputtered sequentially or simultaneously inthe PVD chamber using the shield adjustment discussed above, dependingupon the intended composition of the structure blocking layer 114. Themagnetic reference layer 116 is subsequently deposited on the structureblocking layer 114 at operation 142, and can be formed in a PVD chamberwhere other layers of the MTJ stack 100A may also be formed. This maydepend, for example, upon the composition of other layers such as thebuffer layer 104, if both the buffer layer 104 and magnetic referencelayer 116 are Co_(x)Fe_(y)B_(z)-based. The magnetic reference layer 116can be formed in a PVD chamber using a sputtering target that is aCo_(x)Fe_(y)B_(z) alloy, or by using individual sputtering targets ofCo, Fe, or B, or by a combination of an alloy sputtering target and asingle-element sputtering target, e.g., a CoFe target and a B target.

The tunnel barrier layer 118 is deposited on the magnetic referencelayer 116 at operation 144. In one example of operation 144, the tunnelbarrier layer 118 is formed in a PVD chamber using a metal-oxide targetsuch as MgO in the presence of Ar plasma. In an alternate embodiment,the tunnel barrier layer 118 is formed in the PVD chamber at operation144 using a metal target such as Mg, Ti, Hf, Ta, or Al in the presenceof Ar plasma and O₂ to form the metal-oxide of the tunnel barrier layer118. At operation 146, the magnetic storage layer 120 is formed in a PVDchamber. The formation of the magnetic storage layer 120 can occur invarious ways depending upon the intended composition. The magneticstorage layer 120 can include one or more layers of Co_(x)Fe_(y)B_(z).In some examples, which can be combined with other examples, themagnetic storage layer 120 can include one or more layers of Ta, Mo, W,or Hf. As such, the deposition of the magnetic storage layer 120 in thePVD chamber can include an Ar plasma, a Co_(x)Fe_(y)B_(z) alloy target,individual targets of Co, Fe, and B, or a combination of an alloy targetand an element target such as a CoFe target and a B target. In exampleswhere the magnetic storage layer 120 comprises Ta, Mo, W, or Hf, asputtering target of Ta, Mo, W, or Hf is used in the chamber along withplasma formed from Ar.

In one example, the magnetic storage layer 120 can be formed in a singlePVD chamber in the presence of a plasma formed using Ar by adjusting ashield to expose or protect one or more targets such as those discussedabove that are used to form Co_(x)Fe_(y)B_(z) and layers of Ta, Mo, W,or Hf. In another example, a Co_(x)Fe_(y)B_(z) layer of the magneticstorage layer 120 is sputtered in a PVD chamber using aCo_(x)Fe_(y)B_(z) alloy target in the presence of Ar plasma. In anotherexample, the Co_(x)Fe_(y)B_(z) layer is formed in the PVD chamber usingindividual Co, Fe, and B, targets in the presence of Ar plasma. In stillanother example, the Co_(x)Fe_(y)B_(z) layer is formed in the PVDchamber using an alloy target and an element target, for example, a CoFetarget and a B target, in the presence of Ar plasma. The Ta, Mo, W, orHf layer can be sputtered in the PVD chamber using a Ta target, a Motarget, a W target, or an Hf target.

At operation 148, the capping layer 122 is deposited on the magneticstorage layer 120. In an embodiment, the first capping interlayer 122Aof the capping layer 222 is formed in a PVD chamber that may bedifferent than the PVD chamber where non-oxide layers are formed, asboth Ar plasma and O₂ are present in the PVD chamber during operation148 when oxide layers are formed. The first capping interlayer 122A isdeposited in the PVD chamber by sputtering a Mg target and a plasmaformed from ionized Ar, O₂ is also present in the PVD chamber. Inanother example at operation 148, the first capping interlayer 122A isformed in the PVD chamber using an MgO sputtering target and Ar plasma.In an example where the first capping interlayer 122A is to be formed ofthe same material (e.g., Mg) as the tunnel barrier layer 118, the PVDchamber used for operation 144 can be the same PVD chamber that is usedfor operation 148 to form the first capping interlayer 122A. The secondcapping interlayer 122B is deposited on the first capping interlayer122A at operation 150. Operation 150 can occur in a separate, different,PVD chamber than that used to sputter the first capping interlayer 122Aif O₂ is used in operation 148, since there is no O₂ used in the PVDchamber to form the first capping interlayer 122A. The second cappinginterlayer 122B is formed in a PVD chamber using Ar plasma and one ormore sputtering targets composed of Ru, Ir, and/or Ta. Depending uponthe composition of the second capping interlayer 122B, the operation 150may occur in a PVD chamber that is also used to form, for example, theSAF coupling layer 110 at the operation 136.

Further in the method 1006, at operation 152, a hardmask layer 124 isdeposited over the second capping interlayer 122B in a PVD chamber.Depending upon the type of hardmask layer 124 used in the MTJ stack100A, the operation 152 may or may not occur in the presence of O₂. Forexample, if the hardmask layer 124 is a metal-oxide hardmask, O₂ can beused during operation 152 along with a metallic target or targets toform the metal-oxide layer, or a metal-oxide sputtering target can beused to deposit the hardmask layer 124, in which case O₂ is not used toform the hardmask layer 124 at operation 150. In some embodiments, whenthe hardmask layer 124 is amorphous carbon or spin-on carbon, theoperation 152 in a CVD chamber.

Further in the method 100B, the MTJ stack 100A (or MTJ stack 200 shownbelow in FIG. 2A) formed at operations 128A-152 can be subjected to oneor more processes that are collectively indicated by operation 154 inthe method 1006. These operations can include high-temperature (on theorder of 400° C.) operations. In one example, the processes at operation154 may include a pre-patterning anneal operation, which is followed byan MTJ patterning operation. In an alternate embodiment, the MTJpatterning at operation 154 can include a plurality of processes such aspatterning the hardmask layer 124 and can further include an operationto etch the MTJ stack 100A after the hardmask layer 124 is patterned toform a plurality of individual pillars from the MTJ stack.

In an alternate embodiment at operation 154, a thermal annealingoperation is executed to repair, crystallize, and enhance latticestructures of the film stack, including the magnetic storage layer(s)and the magnetic reference layer(s) in the MTJ stack 100A. The thermalannealing performed at operation 154 can act to further crystallize atleast the material of the magnetic reference layer(s) 116 and magneticstorage layer(s) 120. The crystallization of the magnetic referencelayer(s) and magnetic storage layer(s) upon deposition of those layersestablishes the perpendicular anisotropy of the MTJ stack 100A, whilemaintaining the desired electrical and mechanical properties.Embodiments of MTJ stacks fabricated following the operations of themethod 1006 are shown and discussed below. The embodiments areconfigured to maintain the as-deposited fcc <111> crystalline structureof the pinning layers after the thermal annealing operation executed atoperation 154, and/or during additional or alternate back end processingoperations that occur at high temperatures on the order of 400° C.

The MTJ stacks fabricated according to embodiments of the presentdisclosure employ chromium-based seed layers, including a seed layerincluding at least one of chromium (Cr), nickel chromium (NiCr), ironnickel chromium (NiFeCr), ruthenium chromium (RuCr), iridium chromium(IrCr), or cobalt chrome (CoCr), in contrast to the conventional usageof Ru or Ir for the seed layer. The seed layer is disposed in the filmstack from which the memory cells are defined between a first pinninglayer and a buffer layer. The Cr-containing seed layers discussed hereinimprove adhesion of the first pinning layer because of the latticematching between the seed layer and the first pinning layer which aidsin stabilizing the first pinning layer as well as layers formed on topof the first pinning layer. In one example, the seed layer is in directcontact with both the first pinning layer and the buffer layer, and inother examples, there is a transitional layer between the seed layer andthe first pinning layer or between the seed layer and the buffer layer.The pinning layers discussed herein can be fabricated from cobalt, or asone or more bilayers each of which includes cobalt, or a combination ofa bilayer structure and an overlayer of cobalt, as discussed below. An“overlayer” as discussed herein is a layer formed over another structurethat may include one or more layers, including bilayers. Depending uponthe embodiment, the first and the second pinning layers can include thesame layer structure, materials, and/or thickness, or can vary in layerstructure, materials, and/or thickness. Using the MTJ stacks discussedherein, the crystal structure of the SAF layer and the magnetic couplingof the magnetic reference layer and the magnetic storage layer aresubstantially maintained in a crystalline state, even after annealingthe layers for a period of from 0.5 hours to at least 3 hours at about400° C. Further in the embodiments herein, the MTJ stacks continue toexhibit tunnel magnetoresistance (TMR) from 100% to 175% even afterannealing thereof for 0.5 hours to at least 3 hours at about 400° C.

FIG. 2A is a schematic illustration of an MTJ stack 200 according to anembodiment of the present disclosure. In the illustrated embodiment, abuffer layer 204 is formed via sputtering in a PVD chamber on aconductive portion of a substrate 202, or on a conductive film layer onthe substrate 202. The substrate 202 can include tungsten (W), tantalumnitride (TaN), titanium nitride (Tin), or other metal layers. The bufferlayer 204 improves the adhesion of a seed layer 206 to the substrate202, which aids in the formation and performance ofsubsequently-deposited layers of the MTJ stack 200. The buffer layer 204comprises Co_(x)Fe_(y)B_(z), Ta, and/or TaN, and is formed in one ormore PVD deposition operations in a PVD chamber in the presence of Arplasma. In various examples, the buffer layer 104 is formed in a PVDchamber using Ar plasma and a sputtering target that is aCo_(x)Fe_(y)B_(z) alloy, or by using individual sputtering targets ofCo, Fe, or B, or by a combination of an alloy sputtering target and asingle-element sputtering target, e.g., a CoFe target and a B target. Inan example where a Ta layer is included in the buffer layer 204, the Talayer can be formed in a PVD chamber using a Ta target and Ar plasma.

In one example, the buffer layer 204 comprises TaN and it is sputteredonto the substrate 202 in the PVD chamber using a Ta target in thepresence of both Ar plasma and N₂, the N₂ reacts with the Ta materialsputtered from the Ta target to form the TaN layer. In another example,a TaN sputtering target is used in the PVD chamber with Ar plasma toform the buffer layer 204. In one example, the buffer layer 204 issputtered directly on and in contact with a conductive layer on thesubstrate 202. In other examples, there is a conductive transitionallayer in between the conductive layer on the substrate 202 and thebuffer layer 204 that does not affect performance of the MTJ stack. Thebuffer layer 204 is optionally employed in the illustrated embodiment,and may not be used in some embodiments discussed herein. An overallthickness of the buffer layer 204 is from 0 Å (no buffer layer used) toabout 60 Å. In one example, the buffer layer 204 is a single layer ofTa, TaN, or Co_(x)Fe_(y)B_(z) sputtered directly on, and in contactwith, a conductive layer on the substrate 202 to a thickness of up to 10Å. In another example, the buffer layer 204 is a combination of layers,and each layer of the buffer layer 204 is Ta, TaN, or Co_(x)Fe_(y)B_(z)and is from 1 Å to 60 Å thick. In an example where TaN is employed forthe buffer layer 204 instead of Ta or Co_(x)Fe_(y)B_(z), a thickness canbe 20 Å. In one example where Co_(x)Fe_(y)B_(z) is used alone to formthe buffer layer 204 a layer thickness is 10 Å. In another example ofthe buffer layer 204, Ta or TaN is employed in conjunction withCo_(x)Fe_(y)B_(z), and a thickness of the buffer layer 204 is 20 Å.

The seed layer 206 is deposited in a PVD chamber via sputtering one ormore targets. The seed layer 206 is deposited on the buffer layer 204.The seed layer 206 comprises Cr, NiCr, NiCrFe, RuCr, IrCr, CoCr, orcombinations thereof. The seed layer 206 may be formed as one or morelayers of Cr, NiCr, NiCrFe, RuCr, IrCr, or CoCr, which can includecombinations of those elements or combinations of alloys in a singlelayer. The formation of the seed layer 206 in the PVD chamber isdiscussed in detail above at operation 132. In an embodiment, the seedlayer 206 is 100 Å or less in thickness, and, in one example, the seedlayer 206 is from about 30 Å to about 60 Å thick. In one example, theseed layer 206 is formed directly on and in contact with the bufferlayer 204. In other examples, there is a transitional layer in betweenthe seed layer 206 and the buffer layer 204 that does not affectperformance of the MTJ stack.

Further in the MTJ stack 200, a first pinning layer 208 is formed on theseed layer 206 in a PVD chamber. The formation of the first pinninglayer 208 is shown in detail above at operation 134 of the method 100Bin FIG. 1B, and occurs in a PVD chamber using a plasma of ionized Ar andone or more sputtering targets. In one example, the first pinning layer208 is fabricated as a single layer of cobalt (Co) having a thickness ofabout 1 Å to about 18 Å. In another example, the first pinning layer 208is fabricated from one or more bilayers of various materials, eachbilayer can include two interlayers. The first pinning layer 208 caninclude one or more bilayers alone or in combination with a Co layer, asshown in FIG. 2C. In an example where one or more bilayers are includedin the first pinning layer 208, each bilayer contains a first interlayerof Co and a second interlayer of another element. The first pinninglayer 208 is formed by sputtering a Co target using Ar plasma and,subsequently, sputtering a second target of Pt, Ir, Ni, or Pd using theAr plasma. In an example where Pt is used with Co to form the bilayer,Xe plasma may be used instead of or in addition to Ar plasma. In anembodiment where one or more bilayers are used to form the first pinninglayer, repeated deposition cycles in the PVD chamber can be performed byforming a first interlayer of a bilayer, where the first interlayercomprises Co, by shielding targets that do not include Co. Subsequently,the Co target and other targets are shielded to expose a second targetthat comprises a second element to be used for the second interlayer ofthe bilayer. This may be repeated in an iterative fashion to form one ormore bilayers of the first pinning layer 208. In one example, the firstpinning layer 208 is formed in the PVD chamber directly on and incontact with the seed layer 206. In other examples, there is atransitional layer in between the seed layer 206 and the first pinninglayer 208 that does not affect performance of the MTJ stack.

A synthetic antiferromagnet (SAF) coupling layer 210 is sputterdeposited in a PVD chamber on the first pinning layer 208, and a secondpinning layer 212 is sputter deposited on the SAF coupling layer 210.The SAF coupling layer 210 is formed in the PVD chamber in the presenceof plasma formed from ionized Ar gas using a Ru sputtering target, an Rhsputtering target, a Cr sputtering target, or an Ir sputtering target.The SAF coupling layer 210 comprises a thickness from about 3 Å to about10 Å. In an embodiment, the second pinning layer 212 is fabricated bysputtering a cobalt (Co) target in a PVD chamber in the presence of aplasma formed from ionized Ar gas. In one example, the SAF couplinglayer 210 is formed directly on and in contact with the first pinninglayer 208 and the second pinning layer 212. In other examples, there isa transitional layer in between the SAF coupling layer 210 and either orboth of the first pinning layer 208 or second pinning layer 212 thatdoes not affect performance of the MTJ stack.

The formation of the second pinning layer 212 is shown in operation 138of the method 100B in FIG. 1B above. In an example where one or morebilayers of Co and another element are included in the second pinninglayer 212, the second pinning layer 212 is formed by sputtering a Cotarget using an Ar plasma and, subsequently, sputtering a second targetof Pt, Ir, Ni, or Pd using the Ar plasma. Repeated deposition cycles ina PVD chamber using the Co target and the second target in the presenceof Ar plasma can be used to form the one or more bilayers of the secondpinning layer 212. In one example, the second pinning layer 212 issputtered as a single Co layer from a thickness from about 1 Å to about10 Å. In another example, the thickness of the second pinning layer 212is about 5 Å. Alternate configurations of the second pinning layer 212are shown in FIG. 2D.

Further in the MTJ stack 200, a structure blocking layer 214 isoptionally formed on the second pinning layer 212 by sputtering in a PVDchamber. The structure blocking layer 214 prevents against formation ofa short circuit between the MTJ stack 200 and metallic contacts that canbe coupled to the MTJ stack 200 to form MRAM memory cells. Duringsputtering of the structure blocking layer 214, depending upon theintended composition of the layer, one or more individual Ta, Mo, or Wsputtering targets can be used in the PVD chamber along with an Arplasma. In other examples, during formation of the structure blockinglayer 214, or one or more alloy targets including alloys of Ta, Mo,and/or W can be used in the PVD chamber with the Ar plasma. Thestructure blocking layer 214 is a body-centered-cubic (bcc) structureoriented in the <100> direction, in contrast to the seed layer 206 andthe first pinning layer 208 and the second pinning layer 212 which caneach be oriented in a face-centered-cubic <111> direction. The structureblocking layer 214 is from 0 (no layer) Å to about 8 Å thick, and, inone example, a thickness of 4 Å is sputter deposited. In one example,the structure blocking layer 214 is formed directly on and in contactwith the second pinning layer 212 during sputter deposition. In otherexamples, there is a transitional layer in between the structureblocking layer 214 and the second pinning layer 212 that does not affectperformance of the MTJ stack.

A magnetic reference layer 216 is formed on the structure blocking layer214 by sputter deposition in a PVD chamber in the presence of Ar plasma.The magnetic reference layer 216 can be formed in the PVD chamber usinga single Co—Fe—B alloy sputtering target, or by using two or more of aCo sputtering target, an Fe sputtering target, or a B sputtering target.In another example, the magnetic reference layer 216 can be formed inthe PVD chamber in the presence of Ar plasma using an alloy target andan element target, such as a CoFe target and a B target. The magneticreference layer 216 can be sputtered to a thickness from 1 Å to 15 Å,and, in one example, can be formed to a thickness of 10 Å. The magneticreference layer 216 comprises Co_(x)Fe_(y)B_(z) In one example, z isfrom about 10 wt. % to about 40 wt. %, y is from about 20 wt. % to about60 wt. %, and x is equal to or less than 70 wt. %. In another example,which can be combined with other examples herein, z is at least 20 wt.%. In one example, the magnetic reference layer 216 is formed directlyon and in contact with the structure blocking layer 214. In otherexamples, there is a transitional layer between the magnetic referencelayer 216 and the structure blocking layer 214 that does not affectperformance of the MTJ stack.

A tunnel barrier layer 218 is formed on the magnetic reference layer 216using sputtering of a target in a PVD chamber in an Ar plasma. Thetunnel barrier layer 218 comprises a metal-oxide such as magnesium oxide(MgO), hafnium oxide (HfO₂), titanium oxide (TiO₂), tantalum oxide(TaO_(x)), aluminum oxide (Al₂O₃), or other materials as appropriate forvarious applications. Thus, the tunnel barrier layer 218 can be formedin the PVD chamber in the presence of Ar using a sputtering target of ametal-oxide. Alternately, the tunnel barrier layer 218 can be formed inthe PVD chamber in the presence of Ar and O₂ using a sputtering targetof the metal of the desired metal-oxide, where the metal-oxide layerwhen the metal layer sputtered from the metal sputtering target isexposed to the O₂. The tunnel barrier layer 218 has a thickness from 1 Åto 15 Å, with a thickness of 10 Å in some embodiments. In one example,tunnel barrier layer 218 is formed directly on and in contact with themagnetic reference layer 216. In other examples, there is a transitionallayer between the tunnel barrier layer 218 and the magnetic referencelayer 216 that does not affect performance of the MTJ stack.

In an embodiment, the MTJ stack 200 further comprises a magnetic storagelayer 220 formed on the tunnel barrier layer 218 using a sputteringoperation in a PVD chamber as discussed herein. The magnetic storagelayer 220 can include one or more layers of Co_(x)Fe_(y)B_(z). In someexamples, the magnetic storage layer 220 can alternatively oradditionally include one or more layers of Ta, Mo, W, or Hf. As such,the deposition of the magnetic storage layer 220 in the PVD chamber caninclude using Ar plasma, a Co_(x)Fe_(y)B_(z) alloy target, or individualtargets of Co, Fe, and B, or a combination of an alloy target and anelement target such as a CoFe target and a B target. In examples wherethe magnetic storage layer 220 includes Ta, Mo, W, or Hf, a sputteringtarget of Ta, Mo, W, or Hf is used in the chamber along with a plasmaformed of Ar.

The magnetic storage layer 220 is from about 5 Å to about 20 Å inthickness depending upon factors including a material or materials usedto form the magnetic storage layer 220. In one example, the magneticstorage layer is fabricated from Co_(x)Fe_(y)B_(z) where z is from about10 wt. % to about 40 wt. %, y is from about 20 wt. % to about 60 wt. %,and x is equal to or less than 70 wt. %. In this example, the thicknessof the magnetic storage layer 220 is from 5 Å to 40 Å and, in someembodiments, a target layer thickness is 20 Å. In one example, themagnetic storage layer 220 is formed directly on and in contact with thetunnel barrier layer 218. In other examples, there is a transitionallayer in between the magnetic storage layer 220 and the tunnel barrierlayer 218 that does not affect performance of the MTJ stack. Themagnetic storage layer is shown in FIG. 2E below.

Further in an embodiment of the MTJ stack 200, a capping layer 222 isformed on the magnetic storage layer 220, and includes a plurality ofinterlayers that form the capping layer 222, including an oxide thatcontains iron (Fe). Additionally, in some embodiments, a hard mask layer224 is formed directly on and in contact with the capping layer 222. Inanother example, the hard mask layer 224 is formed on the capping layer222 with a transitional layer in between the capping layer 222 and thehard mask layer 224; such transitional layer does not affect theperformance of the MTJ stack 200. The hard mask layer 224 may be formedof a metal-oxide, amorphous carbon, ceramics, metallic materials, orcombinations thereof. In one example, the magnetic storage layer 220 isformed directly on and in contact with the capping layer 222. In otherexamples, there is a transitional layer between the magnetic storagelayer 220 and the capping layer 222 that does not affect performance ofthe MTJ stack 200. The capping layer 222 is shown in FIG. 2F below.

In one example of the MTJ stack 200, the MTJ stack 200 includes a seedlayer 206 fabricated from NiCr, a first pinning layer 208 fabricatedfrom a Co/Pt bilayer stack, and a second pinning layer 212 fabricatedfrom Co. In this example, the MTJ stack 200 exhibits a TMR of 175%, forexample, when annealed at about 400° C. for 0.5 hours. The TMR of theMTJ stack 200 is maintained at about 175% when the MTJ stack 200 isannealed at about 400° C. for 3 hours.

FIG. 2B is a magnified view of the buffer layer 204 according toembodiments of the present disclosure. The buffer layer 204 includestantalum (Ta) or TaN, or a layered stack of Ta and TaN, and, in someexamples, includes Co_(x)Fe_(y)B_(z), alone or in combination with Ta,TaN, or a Ta/TaN layered stack. In an example of the buffer layer 204,the buffer layer 204 includes at least one bilayer 204D. The at leastone bilayer 204D includes a first buffer interlayer 204A and a secondbuffer interlayer 204B formed in an alternating fashion on the substrate202 for at least one iteration of the at least one bilayer 204D. In thisexample, the first buffer interlayer 204A includes Ta and the secondbuffer interlayer 204B includes TaN, and the first buffer interlayer204A is in contact with the substrate 202. In another example the firstbuffer interlayer 204A includes TaN and the second buffer interlayer204B includes Ta, and thus TaN is in direct contact with the substrate202.

In other examples of the buffer layer 204, as shown in FIG. 2A,Co_(x)Fe_(y)B_(z) is used alone for the buffer layer 204 and would thusbe in direct contact with the substrate 202. In another example, asshown in FIG. 2B, a third buffer layer 204C is formed over the at leastone bilayer 204D. In this example, the third buffer layer 204C isfabricated from Co_(x)Fe_(y)B_(z) and formed to a thickness of up to 10Å. Thus, depending upon the configuration of the buffer layer 204, athickness of the buffer layer 204 ranges from 1 Å thick to 60 Å thick.In an example where the third buffer layer 204C Co_(x)Fe_(y)B_(z) isemployed, z is from about 10 wt. % to about 40 wt. %, y is from about 20wt. % to about 60 wt. %, and x is equal to or less than 70 wt. %.

FIG. 2C is a magnified view of the first pinning layer 208 according toan embodiment of the present disclosure. In an embodiment, the firstpinning layer 208 is fabricated from at least one bilayer 230, and whentwo or more bilayers are employed, the bilayers can be said to form abilayer stack 234. Each bilayer 230 is fabricated from a firstinterlayer 208A and a second interlayer 208B. The bilayers of the firstpinning layer 208 are expressed as (X/Y)_(n), (208A/208B)_(n), whereeach bilayer is a combination of X and Y materials, and n is a number ofbilayers in the first pinning layer 208. In an embodiment, X is Co and Yis one of Pt, Ir, Ni, or Pd. While n=4 in the example in FIG. 2C, inalternate embodiments, n is from 1 to 10. In an embodiment, the at leastone bilayer 230 includes a thickness from about 2 Å to about 15 Å. Inone example, the first interlayer 208A includes Co and is from about 1 Åto about 7 Å thick and the second interlayer 208B is from about 1 Å toabout 8 Å thick. In another example, a desired layer thickness of eachof the first interlayer 208A and the second interlayer 208B is fromabout 2.4 Å to about 5 Å. Further in another embodiment, the firstpinning layer 208 includes the at least one bilayer 230 formed directlyon and in contact with the seed layer 206 in addition to an overlayer208C of Co formed on top of the at least one bilayer 230. In thisexample, the overlayer 208C is from about 1 Å to about 10 Å thick.Depending upon the embodiment, an overall thickness of the first pinninglayer 208, which may include one or more layers including the at leastone bilayer 230 as discussed herein, is from 0.3 nm to about 18 nm. Inother examples, one or more transitional layers may be formed betweenthe first pinning layer 208 and the seed layer 206 that do notnegatively affect the properties of the MTJ stack.

FIG. 2D is a magnified view of the second pinning layer 212 according toembodiments of the present disclosure. In an embodiment, the secondpinning layer 212 is fabricated from a single cobalt layer as shown inFIG. 2A. In alternate embodiments, the second pinning layer 212 isfabricated from at least one bilayer 232. The at least one bilayer 232includes a first interlayer 212A formed from Co and a second interlayer212B formed from one or more of Pt, Ir, Ni, or Pd. When two or morebilayers such as the bilayer 232 are employed in the second pinninglayer 212, the plurality of bilayers may be referred to as a bilayerstack 236. Thus, at operation 138 in FIG. 1B, when one or more bilayersare used, a separate sputtering target may be used to form each layer ofthe bilayer. The at least one bilayer 232 of the second pinning layer212 is expressed as (X/Y)_(n), (212A/212B)_(n), where n is a number ofbilayers. While n=4 in the example in FIG. 2D, in alternate embodiments,n is from 1 to 10. In an embodiment, the at least one bilayer 232includes a total thickness from about 2 Å to about 15 Å. In one example,the first interlayer 212A is a Co layer from about 1 Å to about 7 Åthick and the second interlayer 212B is from about 1 Å to about 8 Åthick. In another example, thickness of each of the first interlayer212A and the second interlayer 212B is from about 2.4 Å to about 5 Å.

Further in another embodiment, the second pinning layer 212 includes atleast one bilayer 232 formed directly on and in contact with the SAFcoupling layer 210 in addition to an overlayer 212C of Co on top of theat least one bilayer 232. In some examples, a transitional layer may beemployed between the at least one bilayer 232 and the second pinninglayer 212 or between the at least one bilayer 232 and the SAF couplinglayer 210, or both, where such transition layer(s) do not affectperformance of the MTJ stack. In this example, the overlayer 212C isfrom about 1 Å to about 10 Å thick. Depending upon the embodiment, anoverall thickness of the second pinning layer 212, which may include oneor more layers including the at least one bilayer 232 as discussedherein, is from 0.3 nm to about 18 nm.

In an embodiment, the first pinning layer 208 and second pinning layer212 each include at least one of the same composition or the samethickness. In an alternate embodiment, the first pinning layer 208 andsecond pinning layer 212 each include different compositions and/orthicknesses. In an embodiment, the first pinning layer 208 is Co and thesecond pinning layer 212 is formed from one or more bilayers. Eachbilayer of the second pinning layer 212 includes a first interlayer ofCo and a second interlayer of Pt. In another embodiment, the firstpinning layer 208 is Co and the second pinning layer 212 is formed fromone or more Co/Ni bilayers. In yet another embodiment, the first pinninglayer 208 includes one or more bilayers, each bilayer containing a firstinterlayer of Co and a second interlayer of Ni, and the second pinninglayer 212 includes one or more bilayers, each bilayer containing a firstinterlayer of Co and a second interlayer of Pt. In yet anotherembodiment, the first pinning layer 208 includes one or more bilayers,each bilayer containing a first interlayer of Co and a second interlayerof Pt, and the second pinning layer 212 includes one or more bilayers,each bilayer containing a first interlayer of Co and a second interlayerof Ni.

FIG. 2E is a magnified view of an example magnetic storage layer 220according to embodiments of the present disclosure. As shown in FIG. 2E,a first magnetic layer 220A of the magnetic storage layer 220 and asecond magnetic layer 220B of the magnetic storage layer 220 are eachfabricated from Co_(x)Fe_(y)B_(z). A third layer 220C fabricated fromTa, Mo, W, Hf, or combinations thereof is disposed therebetween, and itcontains dopants such as boron, oxygen, or other dopants. The magneticstorage layer 220 is thus fabricated from three layers, a first magneticlayer 220A and a second magnetic layer 220B, and a third layer 220Cdisposed between the first magnetic layer 220A and the second magneticlayer 220B. The third layer 220C strengthens a pinning momentperpendicular to the substrate plane (e.g., a plane perpendicular to thesubstrate 202), which promotes magnetic anisotropy, a directionaldependence of the structure's magnetic properties.

FIG. 2F is a magnified view of an example capping layer 222 according toan embodiment of the present disclosure. A total thickness of thecapping layer 222 is from 2 Å to 120 Å and in some embodiments a totaldesired thickness for the capping layer (e.g., including all interlayersas shown in FIG. 2F) is about 60 Å. In an embodiment, the capping layer222 includes a plurality of interlayers. A first capping interlayer 222Ais fabricated from MgO or another iron-containing oxide formed directlyon the magnetic storage layer 220 to a thickness from about 2 Å to about10 Å. On top of the first capping interlayer 222A, a second cappinginterlayer 222B of Ru, Ir, or combinations thereof is formed to athickness from 1 Å to about 30 Å. In an embodiment, a third cappinginterlayer 222C is optionally formed of Ta on the second cappinginterlayer 222B to a thickness of 1 Å to about 30 Å. Thus, someembodiments of a capping layer 222 do not contain a third cappinginterlayer 222C. In an embodiment, a fourth capping interlayer 222D isoptionally formed on the third capping interlayer 222C and is formed ofRu, Ir, or combinations thereof to a thickness of up to 50 Å. In variousembodiments, the capping layer 222 includes only the first cappinginterlayer 222A, or the first capping interlayer 222A and the secondcapping interlayer 222B, or the first capping interlayer 222A, thesecond capping interlayer 222B, and a third capping interlayer 222C, orthe first, second, and third capping layers 222A-222C. In someembodiments, transitional layers may be used in between some or all ofthe first capping interlayer 222A, the second capping interlayer 222B,and the third capping interlayer 222C, or may be between the cappinglayer 222 and the magnetic storage layer 220, such that the performanceof the MTJ stack is not negatively impacted by the transitionallayer(s).

The MTJ stacks discussed herein have improved performance afterundergoing processing at temperatures at or above 400° C. The improvedperformance is promoted by the lattice matching between the structure ofthe seed layer and of the first pinning layer as a result of using a Crseed layer or a Cr-containing seed layer in combination with the firstpinning layer that also includes Cr. The lattice matching between thestructures of the seed layer and the first pinning layer inhibitsroughness formation at the interface of the seed layer and the firstpinning layer, such roughness formation results in a lack of flatness inone or more layers. The MTJ stacks are thus able to maintain structuralintegrity as well as desirable magnetic and electrical properties.Further in the embodiments discussed herein, the combinations of firstand second pinning layer compositions with the seed layer can increasedesirable magnetic properties even after high temperature processing.

While the foregoing is directed to embodiments of the presentdisclosure, other and further embodiments of the disclosure may bedevised without departing from the basic scope thereof, and the scopethereof is determined by the claims that follow.

What is claimed is:
 1. A magnetic tunnel junction stack comprising: abuffer layer; a seed layer formed on the buffer layer, the seed layercomprising chromium (Cr); a first pinning layer in direct contact withthe seed layer, the first pinning layer comprising at least one bilayer,the at least one bilayer comprising: a first interlayer formed fromcobalt (Co); and a second interlayer formed from platinum (Pt), iridium(Ir), nickel (Ni), or palladium (Pd); and a second pinning layer formedover the first pinning layer, wherein the buffer layer, the seed layer,the first pinning layer and the second pinning layer form a portion ofthe magnetic tunnel junction stack.
 2. The stack of claim 1, furthercomprising: a magnetic reference layer in formed over the second pinninglayer; a tunnel barrier layer formed over the magnetic reference layer;a magnetic storage layer formed over the tunnel barrier layer; acoupling layer in direct contact with the first pinning layer and thesecond pinning layer; and a structure blocking layer in direct contactwith the second pinning layer.
 3. The stack of claim 1, wherein thebuffer layer is comprises Co_(x)Fe_(y)B_(z).
 4. The stack of claim 1,wherein the buffer layer is comprises tantalum (Ta).
 5. The stack ofclaim 1, wherein the buffer layer comprises Co_(x)Fe_(y)B_(z), tantalum(Ta), tantalum nitride (TaN), or combinations thereof.
 6. The stack ofclaim 5, wherein the buffer layer comprises a plurality of layers, andwherein each layer of the plurality of layers comprisesCo_(x)Fe_(y)B_(z), tantalum (Ta), or tantalum nitride (TaN).
 7. Thestack of claim 6, wherein each layer of the plurality of layers has athickness between about 1 Å and about 60 Å.
 8. The stack of claim 1,wherein the seed layer comprises nickel chromium (NiCr), iron nickelchromium (NiCrFe), ruthenium chromium (RuCr), iridium chromium (IrCr),cobalt chrome (CoCr), or a combination thereof.
 9. The stack of claim 8,wherein the seed layer comprises a plurality of layers, and wherein eachlayer of the plurality of layers comprises nickel chromium (NiCr), ironnickel chromium (NiCrFe), ruthenium chromium (RuCr), iridium chromium(IrCr), or cobalt chrome (CoCr).
 10. The stack of claim 1, wherein theseed layer has a thickness of about 100 Å or less.
 11. The stack ofclaim 10, wherein the seed layer has a thickness between about 30 Å andabout 60 Å.
 12. A magnetic tunnel junction stack comprising: a bufferlayer comprising Co_(x)Fe_(y)B_(z), tantalum (Ta), tantalum nitride(TaN), or combinations thereof; a seed layer formed in direct contactwith the buffer layer, the seed layer comprising chromium (Cr); a firstpinning layer in direct contact with the seed layer, the first pinninglayer comprising at least one bilayer, the at least one bilayercomprising: a first interlayer comprising cobalt (Co); and a secondinterlayer comprising platinum (Pt), iridium (Ir), nickel (Ni), orpalladium (Pd); a second pinning layer formed over the first pinninglayer, the second pinning layer comprising at least one bilayer; amagnetic reference layer in formed over the second pinning layer; atunnel barrier layer formed over the magnetic reference layer; and amagnetic storage layer formed over the tunnel barrier layer.
 13. Thestack of claim 12, wherein the seed layer is nickel chromium (NiCr),iron nickel chromium (NiCrFe), ruthenium chromium (RuCr), iridiumchromium (IrCr), cobalt chrome (CoCr), or a combination thereof.
 14. Thestack of claim 12, wherein the buffer layer comprises a plurality oflayers, and wherein each layer of the plurality of layers comprisesCo_(x)Fe_(y)B_(z), tantalum (Ta), or tantalum nitride (TaN).
 15. Thestack of claim 14, wherein each layer of the plurality of layers has athickness between about 1 Å and about 60 Å.
 16. The stack of claim 12,wherein the seed layer comprises a plurality of layers, and wherein eachlayer of the plurality of layers comprises nickel chromium (NiCr), ironnickel chromium (NiCrFe), ruthenium chromium (RuCr), iridium chromium(IrCr), or cobalt chrome (CoCr).
 17. The stack of claim 12, wherein theseed layer has a thickness of about 100 Å or less.
 18. The stack ofclaim 17, wherein the seed layer has a thickness between about 30 Å andabout 60 Å.
 19. A magnetic tunnel junction stack comprising: a substratehaving a buffer layer formed thereon, the buffer layer comprisingCo_(x)Fe_(y)B_(z), tantalum (Ta), tantalum nitride (TaN), orcombinations thereof; a seed layer formed over the buffer layer, theseed layer comprising chromium (Cr), nickel chromium (NiCr), iron nickelchromium (NiCrFe), ruthenium chromium (RuCr), iridium chromium (IrCr),cobalt chrome (CoCr), or a combination thereof; a first pinning layer indirect contact with the seed layer, the first pinning layer comprisingat least one bilayer, the at least one bilayer of the first pinninglayer comprising: a first interlayer comprising cobalt (Co); and asecond interlayer comprising platinum (Pt), iridium (Ir), nickel (Ni),or palladium (Pd); a coupling layer in contact with the first pinninglayer; a second pinning layer formed over the coupling layer, the secondpinning layer comprising at least one bilayer, the at least one bilayerof the second pinning layer comprising: a first interlayer comprisingcobalt (Co); and a second interlayer comprising platinum (Pt), iridium(Ir), nickel (Ni), or palladium (Pd); a magnetic reference layer informed over the second pinning layer; a tunnel barrier layer formed overthe magnetic reference layer; and a magnetic storage layer formed overthe tunnel barrier layer.
 20. The stack of claim 19, wherein the seedlayer comprises a plurality of layers, and wherein each layer of theplurality of layers comprises nickel chromium (NiCr), iron nickelchromium (NiCrFe), ruthenium chromium (RuCr), iridium chromium (IrCr),or cobalt chrome (CoCr).